In connection with conventional propeller fans, for example, Japanese Patent Laying-Open No. 3-88999 has disclosed an axial fan aimed at increasing lift of propeller blades and also improving strength thereof by supplying, in a separated fashion, positive and negative pressures to positive and negative pressure surfaces of each propeller blade, respectively (PTL 1). The axial fan disclosed in PTL 1 has a plurality of propeller blades that are formed on the outer periphery of a hub and extend radially outward from an axis of the hub.
Further, Japanese Patent Laying-Open No. 2000-314399 has disclosed a propeller fan aimed at eliminating necessity of post treatment on a boss portion at a rotation axis aperture portion, and improving gate processing (PTL 2). The propeller fan disclosed in PTL 2 has a cylindrical or conical hub portion, and blade portions formed integrally with the hub portion.
Furthermore, various propeller fans have been disclosed in Japanese Patent Laying-Open No. 64-397 (PTL 3), Japanese Patent Laying-Open No. 2008-240526 (PTL 4), and Japanese Patent Laying-Open No. 2004-132211 (PTL 5).